<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <title>Document</title>
    <style>
        * {
            margin: 0;
            padding: 0;
        }

        #left {
            width: 200px;
            /* 定宽 */
            height: 300px;
            background-color: #c9394a;
            float: left;
        }

        #center {
            width: 200px;
            /* 定宽 */
            height: 300px;
            background-color: green;
            float: left;
        }

        #right {
            height: 300px;
            background-color: pink;
            margin-left: 400px;
        }
    </style>
</head>

<body>
    <div id="parent">
        <div id="left"></div>
        <div id="center"></div>
        <div id="right"></div>
    </div>
</body>

</html>